SUMMARY The metabolomics core laboratory at the Duke Stedman Center deploys both targeted and non-targeted mass spectrometry (MS)-based metabolic profiling to provide a rare combination of broad coverage and analytical precision. The Duke team has been a leader in applying targeted MS-based metabolic profiling for understanding of disease and biological mechanisms. The role of the core in the current application will be to perform both targeted and non-targeted metabolomics assays on samples generated by Dr. Gordon in Project 1, and Drs. Heath and Klein in Project 2; in both instances this work continues previously established and productive collaborations between our groups. In the context of Project 1, Core A will measure metabolites produced by microbial communities taken from obese and lean twin pairs and transplanted into germ-free mice, and will also provide metabolomic profiles of serum, urine and tissues of the host animals. In the context of Project 2, Core A will provide metabolomic profiles of twin pairs with discordance for obesity that are further sub-divided into metabolically well and unwell subgroups. Obtaining metabolic profiles of the human subjects in collaboration with Project 2 provides a unique opportunity to investigate the impact of gut microbiota from those subjects on metabolism when transplanted into mice via Project 1. We hypothesize that disease-related metabolic signatures will be transmitted to germ-free mice by transplantation of microbial communities from obese and metabolically unhealthy subjects. Metabolic profiles of serum, urine and tissues will include targeted MS/MS and GC/MS-based assays of approximately 220 metabolites across 8 classes or modules of analytes that represent byproducts of core metabolic pathways. These analyses will be supplemented by non-targeted GC/MS-based analyses of a broader array of metabolites, including some unique to microbial metabolic pathways.